System for amplifying variable currents.



L LANGMUIR.

SYSTEM FOR AMPLIFYING VARIABLE CURRENTS.

IHXPPLICATION FILED OCT. 29, I913.

L fiwu Patented. 00. 22,1918.

WZTNESEES jinx YENTQH,

j M YREZ'JJVE' LANQWE E15 $2? 1 03mm IRVING LANGMUIR, 0F SCHENECTADY, NEW YORK, ASSIGN OR TO GENERAL ELECTRIC COMPANY, LA -CORPORATION OF NEW YQRK.

SYSTEM FOR AMPLIFYING VARIABLE CURREN TS.

Specification of Letters Patent. Patented Oct, 22, 1918,

Application filed October 29, 1913. Serial No. 797,985.

7 '0 all whom 1'2- m (13 concern:

Be it known that I, IRVING LANGMUIR, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Systems for Amplifying Variable urrents, of which the following is a specificat on.

The present, Invention relates to electrical discharge apparatus utilizing an electron discharge and comprises novel systems of connection whereby teak variable currents may be reproduced as stronger currents. My invention also includes means fonsecuring selectivity in detecting s1 g11als, for example, for receiving systems in radio-teleg- Tlie electron-discharge device preferably utilized in accordance with my invention comprises an inczmdescent, or other electronemitting cathode, a cooperating gas-free anode and a discharge-controlling conductor, commonly called thegrid, and an inclosing envelop, the space in the envelop being evacuated below the pressure at wlnch appreciable gas lomzatlon by coll1s1on w1th electrons can occur, as descrlbed and claimed in my prior application, Serial No. 795,610

filed Oct. 16, 1913. but it is to be understood that my invention is not limited to this particular apparatus.

My invention includes a combination of two or more electron discharge devlces con nected in cascade, the electrode circuit of one device being connected to a resistance, a reactance or transformer across which is connected the grid circuit of a second device. My invention also includes other novel features, such as means for integrat1ng high frequency wave trains into impulses or Waves of lower frequency, tuning both for group frequency as well as wave frequency, and other features pointed out with greater particularity in the appendedclaims.

A more detailed understandm of my 111- vention may be had from the folowing description taken in connect on with the accompanying drawings, which show for'the purpose of illustrat1on my invention a plied to receiving 6 stems of wireless telegraphy. Figure 1 ilustrates a system con-" a device havlng an lllummated' tainin catho e; Fig. 2 lllustrates a tuned system containing a condenser for integrating 0scillations, and Fig. 3 is'a diagram illustrating an integrating effect secured with a condenser with the 'rid circuit.

In Fig. 1 an electron discharge device A comprises a gas-tight envelop 1 which may consist of quartz or glass, preferably material pervious to ultra-violet light, and into which aresealed in the usual manner an such as mercury vapor arc in a quartz or glass envelop is advantageous in giving electrons of uniform velocity, The anode preferably consists of tungstenandis do; prived of gas by electron bombardment during the exhausting process, the envelop be mg oughly freed from gas and the pressure in the envelop has been reduced to a value at which noappreciable gas ionization can occur. The grid 4 and the cathode 2 'are connected respectively by conductors Sand 7 to the secondary of a transformer 8, the primary of which is located in circuit with an antenna 9. In the antenna circuit there may be located a grounded condenser 10 but the antenna. connections and structure may be the usual ones forn'iing no part of my present invention. In the grid circuit '7, there is preferably included a source of o tential '11, such as a battery which preferably is connected to maintain the grid at a definite negative potential, but in some cases the grid may be maintained at a positive potential.

electron. emitting cathode 2, a cooperating sealed when the anode has been thorg In the circuit connecting the cathode and r V respectively by may be placed a condenser 24. In some cases a battery or other source of potential may be included in the grid circuit 17 This method of connecting two amplifiers in cascade is claimed in my application, Serial No.

' 11,512, filed March 2, 1915, which is a divielectromagnetic sion of this application.

In the system described the discharge device A, which may haverelatively large distances between the grid and the electrodes, is made very sensitive to changes of grid voltages. The fact that the electrons are emitted by the ,cathodeat uniform velocity contributes to its sensitiveness. A comparatively feeble impulse received from the antenna 8 will be accompanied by a change in the current from the local source 12 through the resistance 13. The current increases when a positive wave is superimposed on.

the negative grid potential. The current flowing through the resistance 13 will be greater than the current received from the antenna, and therefore, will produce greater variations in the static charge of the grid 16 of the device B than were originally received by the grid 4 of the device A. Hence, these potentials may be used to produce greatly amplified signal current. In other words, the stronger currents flowing in the electrode circuit of the device A can be used to vary the flow of electron discharge current betweenthe cathode 14 and the anode 26 of the discharge device B which is adapted to control relatively a greater amount of energy than the device A although not necessarily so sensitive to minute voltage changes as the device A. This feature of my invention is claimed in my application Serial N0. 254,334, filed Sept. 16, 1918,

which is a division of this application.-

When the switch 19 is set so as to connect the positive terminal of the resistance 13 to the grid circuit 17 containing means for making the grid 16 negative, an increase of plate current of device A will produce an increase in the plate current of device The converse is the case when the connections are reversed. The variations in the electrode or plate circuit constitutes further amplification of the original signal currents and may be made great enough to-operate an instrument 23, such as a telegraph relay, or in any convenient way to indicate the signals. In some cases an ordinary telephone may be connected to the terminals of the conductors 20, 21, to detect I the amplified signals.

The system shown in Fig. 2 is in some respects similar to the system shownin Fig. 1, for example, in the character of the discharge device used, and therefore need not be again described in detail. Each device has a heated cathode 0 and an unheated an- ,ode a, both of which may consist of tungof operation will be better understood by first considering the connections and then tracing through the method of operation.

' The grid 27 of the discharge tube M is connected to the secondary ,of the loosely coupled air core transformer 28. The primary of the transformer is included in a grounded antenna circuit similar to that shown in Fig.

1. In the grid circuit 29 is included a source of potential 30 and across the transformer secondary is connected a condenser 31, which preferably is made adjustable. By properly proportioning the inductance of the transformer-secondary and the capacity of the condenser, the oscillating circuit constituted thereby may be made-resonant to a desired frequency and therefore will be largely opaque to disturbances. Hence the grid will be influenced only to a slight extent by frequencies differing from the desired predetermined frequency. As already explained the variations in the grid potential, which is preferably negative, produced by the impressed oscillations result in oscillations in the plate circuit 32 similar to those in the grid circuit. These oscillations having been produced by a local source of current 33 may be stronger than the received oscillations. They are impressed on another oscillating circuit 34, 35, by means of an air core transformer 36. The circuit 34, 35, is likewise adjusted to be opaqnetq undesired oscillations by properly adjusting the condenser 37. The oscillations produced in the plate circuit 38 of the device R by a local source of energy 39 are again transmitted to another local oscillating circuit 40 which is also tuned, by an air core transformer 41. It will be noted that by thus tuning successive circuits the ture tuning for both oscillation frequencyand group frequency, as will be explained. The grid circuit 42 of the discharge tube S contains a condenser 43 which is shunted by a high resistance 44- and battery 45.wh1ch preferably has its negative terminal con;

nected to the grid 46. Both the resistance and the battery are pr'orided with an adjustable shunt 47 so that the potential of the battery and amount of resistance may be both varied or, in fact, entirely eliminated. Even when the grid 46 is not maintained at a predetermined potential it will assume some negative potential as it receives electrons from the cathode a and its potential is de termined by thesurface of the gridlfi and the rate at whichthe charge may leak ofi from the condenser plates. When the grid is positively charged it will take up electrons at a rate varying with the degree'of positive charge and when the grid is negatively charged the rate at which it absorbs electrons decreases With the degree of negative charge until a value is reached at which no more eLectrons are taken up. The condenser charge will come to an equilibrium wheir the rate of leakage is equal to the rate of charge ing by the electrons absorbed. This grid potential may be assumed to have a negative Y value represented by the. line 77 in Fig. 3 which represents a diagram in which the ordinates are grid potentials and the abscissa: represent time. The actual number of oscillations in each group, of course, will be much greater than indicated in Fig. 3. When the oscillations are superin'iposed on the grid, assuming its potential to be 7), Fig. 3, a positive Wave 48 will cause it to take up more electrons, which are not discharged during the succeeding negative wave. Each successive wave adds its increment to the negative charge Which thus accumulates on the grid and the plate of the condenser connected to it. After a certain number of oscillations have thus been received the grid has received such a negative charge that it no longer takes up more electrons than it loses. When the wave train ceases, the added negative charge leaks oil as indicated by the line 50, until the grid potential again assumes its original value 7). The capacity of the condenser 43, the potential of the battery 45, if one is used, and the resistance 44 should be i so chosen that the grid 46 will have resumed its equilibrium charge before the next wave train is impressed on it.

As the current in the plate circuit 51 of the tube S is determined by the grid charge,

' a variable current will tend to flow therein having a frequency equal to the group freaaeaeae quency of the signals received from the antenna and also having a high frequency component. The hi h. requenc'y component of this current may e eliminated by making the circuit responsive or resonant end to the lcw freuency. This may be done y providing t e transformer 52 with an iron core as to introduce considerable inductance into the circuit 51 and also by shunting the primary circuit of the transformer with a condenser 53. A relatively smooth low frequenc alternating current will flow in the secon ary circuit 54: Which may be tuned'for the frequency to be selected by an adjustable condenser 55. l A

The selectivity of thesystem thus is made very great as it is'opaque not only to disturbances having a difi'erent frequency than the oscillations to be received but is also opaque to aerial signalshavinga difierent group of frequency. The number of circuits connected thus in series or in cascade may be increased to any desired number.

In the system illustrated the oscillations of, the circuit 54 are impressed on a grid 56, in circuit with which preferably is a.-

source of potential 57. The currents in the plate circuit 58 produced by a local source- 59, are varied as already explained by variations of grid potential. The amplified and by Letters Patent of the United States is selected si als may be recorded or detected l. A selective system for detecting signals consisting of groups of high frequency oscillations, comprising the combination of a plurality of circuits resonant to the frequency of the oscillations to be selected, relay means interposed between said respective circuits and operative to impress upon one circuit oscillations proportionate to oscillations in another circuit, means for integrating the high frequency oscillations in one of said circuits to produce a variablecurrent having a frequency equal to the group frequency of the signals, a circuit connected thereto resonant to said group frequency and means for detecting current in said circuit.

2. A- selective system for detecting signals consisting of a group of high frequency oscillations comprising a plurality of circuits, electron discharge devices connected to link said circuits in cascade, a local source of energy in circuit with each of said discharge devices, a series condenser included in the grid circuit of one of said discharge devices and means for detecting current in denser and a local source of energy coiinected in circuit with the electrodes of said device.

4, The combination of a device operating with a substantially pure electron discharge, a grid for controlling the electron discharge,

- a condenser in circuit with said grid, a circuit shunting said condenser, a reslstance and a battery in said circuit, means for varying the potential of said battery and amount of said resistance, and a local source of energy in the electrode circuit of said device.

5. A system for selecting groups of high frequency oscillations from dlsturbing oscillations comprising the combination of a cir-' cuit resonantto the frequency of the oscil- 'lat-ions to be selected, a second circuit resonant to the group frequency of said oscillations, relay means interposed between said circuits operative to impress upon the second circuits amplified oscillations proportionate to oscillations in the first circuit and means for receiving and detecting a current in the second circuit.

.6. The combination of an electron discharge device having an electron-emitting cathode, a coiiperating anode and a grid for controlling the electron discharge, a condenser connected in circuit with said grid and a high resistance connected'in shunt to said condenser.

7. The combination of an electron dis- I v charge device havinglan electron emitting I cathode, a .,'co6peratmg anode and a grid for controllingthe electron dischargda con-' denser connected in series relation in the grid circuit of said device, and a source of potentlal connected in shunt to said condenser. a i

8. The combination of an electron discharge device having an electron-emitting cathode, a coiiperating anode. and a grid for controlling the electron discharge, a com denser in circuit with said grid and a cir-.

cuit shunting said condenser, said circuit comprising a source of potential and a high resistance. a y l 9. The combination of an electron discharge device havin an electron emitting cathode, a plate anode, and a grid ixiclosed in a receptacle evacuated to such a degree that the device will operate with substantially no gas-ionization, grid and plate circuits for said device, means 'for impressing upon the grid circuit groups of high fre-" quency oscillations, and means for integrating the high frequency oscillations to produce in the plate circuit a variable current ,having a frequency equal to the roup frequency of the highfrequency osci lations.

1-0'. The combination of an electron dis-* 7 charge device having an electron emitting cathode, an anode and a grid inclosed in a receptacle evacuated to such a degree'that the device will operate with substantially no gas ionization, a condenser connected in circuit with said grid, and a high resistance connected in shunt to said condenser. I

In witness whereof, I have hereunto set my hand this 27th day of October, 1913.

IRVING LANGMUIR. Witnesses:

, SAUL DUSHMAN, HELEN ORFORD. 

